This invention relates to a device for temporarily implanting, in a vein of the human body, and in particular in the inferior vena cava of a patient, a blood filter, and more particularly a blood filter of the type that is elastically expandable in the radial direction.
The function of blood filters is to hold back the blood clots that may form in the course of phlebitis or other vascular or cardiovascular disorders, in order to prevent their migration towards the pulmonary arteries where they could cause an embolism.
The filters generally used for this purpose have the shape of a small umbrella consisting of a plurality of flexible branches that can be radially expanded. In the rest position (retracted state) the branches extend approximately parallel to one another and occupy a reduced dimension in the radial direction, and this allows them to be positioned in a vein. Once in place inside the vein, the branches spread automatically outward and are immobilized against the wall of the vein, thereby anchoring the filter at the desired site.
Filters of this type are preferably positioned in the inferior vena cava, a little below the level of the kidneys.
The equipment that permits positioning of the filter traditionally comprises a guide rod and a mandrel which make it possible to insert a sheath into the vein to the desired depth, in such a way that the end of the sheath arrives at the site where the filter is to be positioned. When the filter is positioned in the inferior vena cava, it is known to carry out the implanting via a percutaneous access route or by "denudation" at the level of the right internal jugular vein. The positioning is thus carried out starting from the jugular vein, and via the superior vena cava. After the sheath is positioned, the mandrel and the guide rod are withdrawn. The filter is then introduced into the sheath by a special syringe and displaced inside the sheath, along its entire length, by the mandrel, the latter in this case having the role of a pusher. When the filter arrives at the free end of the sheath (previously positioned at the desired site in the inferior vena cava), the filter spreads open automatically and anchors in the wall of the vein. The sheath is then removed, and the filter remains permanently in position.
The main disadvantage of this technique is that the filter can be withdrawn only by performing a very delicate surgical operation. Unfortunately, the permanent positioning of the filter in the vena cava is a source of complications, in particular, the filter can trigger a thrombosis. Moreover, the patient with this filter in place must take anticoagulant medication for life.
These disadvantages are all the more regrettable since, in a great many forms of treatment, the positioning of the filter in the vein is necessary only for a limited period, generally a few weeks or a few months, corresponding to the period during which there is a real risk of embolism.
For this reason a technique has recently been proposed for implanting the filter temporarily and removably, so it can be withdrawn after a certain time has elapsed.
For this, the mandrel which is used for implanting the filter is permanently integral with the latter; after the filter is implanted, the mandrel remains inserted in the vein and projects from the body via the access route used for the implanting, that is, at the level of the neck, in the region of the jugular vein, when the filter is implanted in the vena cava. Unfortunately, such a rod, which is relatively rigid, is very uncomfortable for the patient; moreover, because the mandrel projects from the skin, it constitutes a source of infection that may lead to serious complications, especially septicaemia.